This invention relates generally to the field of remotely monitored identification devices using electromagnetic waves. More particularly, it relates to interrogating radio-frequency identification devices.
Generally, radio-frequency identification devices (RFID) are used in multiple asset tracking applications e.g., automotive, airline baggage, consumer items, food items, garments, livestock etc., including numerous medical and military applications.
Some types of RFID devices rely on internal power for operation, such as a battery, for powering a semiconductor chip, and/or converts part of the received radio-frequency (RF) signal to electrically power the semiconductor chip. Unfortunately, typical semiconductor chips used for example in RFID devices that rely on internal power consume tens of microwatts of power, which is a considerable fraction of the total RF power captured by the antenna of the RFID device. In addition, the process of attaching the chip to a carrier and subsequent bonding to the antenna takes several manufacturing steps that add to the cost of the RFID device.
Conventional RFID devices with semiconductors chips generally operate over a narrow band of frequencies, making them susceptible to problems of multipath propagation and interference. In addition, such RFID devices do not carry range or location information. Such issues make it extremely difficult to locate conventional RFID devices especially in a cluster of RFID devices.
Chipless read-only RFID devices have been developed by the industry to overcome some of the disadvantages of RFID devices with semiconductors chips. Such chipless read-only RFID devices have the advantage of not requiring any semiconductor circuitry in the RFID device and therefore do not rely on an internal power source but rely on reflecting a portion of the RF using the principle of “passive backscatter”.
One way to construct these types of Chipless RFID devices is by embedding metallic fibers in material like paper, and observe the resonances in millimeter wave for identification. Unfortunately, such conventional passive chipless read-only RFID devices are difficult to discern in the presence of other similar chipless read-only RFID devices.
Therefore what is needed is method and apparatus that allows a user to discern one or more RFID devices in proximity to other RFID devices that is simple to implement and cost effective.